1. Field of the Invention
The present invention generally relates to systems for the production of oil and gas, and more specifically, to a method and to an apparatus for enhancing the secondary and tertiary recovery of oil and gas.
In its infancy, the United States petroleum production industry experienced drilling excesses and overproduction, and accelerated the depletion of major oil and gas reserves. Careless drilling and production practices led not only to waste, but also to contamination. Frequently, such contamination was evidenced by extensive clogging of existing wells due to water infiltration, paraffin buildup, or to the formation of emulsions within the wells. Such fouling decreased the yield and made further production uneconomical. As a result, wells which contain significant reserves of oil and gas have been abandoned. There has been a long standing need to establish an efficient and economical method for enhancing the recovery of oil and gas from marginally producing wells.
The traditional method for the recovery of oil and gas from underground formations includes the use of drilling equipment, fracturing equipment, and pumping equipment. The aforementioned method is termed "primary recovery," because the recovery of the hydrocarbon depends on the pressure energy initially present in the reservoir. The pressure energy contained within the formation provides the force necessary to enable the oil and gas to migrate horizontally into producing wells for recovery. When this energy has been depleted, and the rate of oil recovery becomes uneconomical, oil production can only be increased through the injection of secondary energy into the reservoir. The injection techniques employed are designated as "secondary recovery," because the injection of fluids results in a second phase of oil production. Conventional methods of secondary recovery encompass immiscible displacement processes, such as water flooding and gas injection. After secondary recovery, substantial quantities of oil frequently still remain in the reservoir. Processes that aid in the recovery of oil beyond the primary and secondary recovery methods are referred to as "tertiary recovery" methods.
Tertiary recovery processes entail substantial risk in view of the technical sophistication and "front-loaded" financial investment required. Tertiary processes include such techniques as miscible fluid displacement (carbon dioxide injection), micro-emulsion flooding, thermal flooding (steam flooding or in situ combustion) methods, and other chemical flooding (alkaline or surfactant) methods. All of the above listed methodologies are referred to as "enhanced oil recovery processes." Of available enhanced oil recovery methods, steam injection and in situ combustion have enjoyed the greatest success.
When steam is injected down the well bore and into the formation, steam increases bottom hole pressure and the gravity of the oil, and decreases the viscosity and surface tension of the oil. This method releases more of the oil and gas from the underground formation, enhancing recovery. Steam injection techniques commonly generate temperatures of from about 82.degree. C. to about 248.degree. C. and pressures of from about 500 psi to about 1,500 psi. However, steam injection is by no means free from significant problems. Before one can undertake such a project, the following considerations must be taken into account: availability of water; required water treatment; possible recycling of product water; stack gas cleanup; production treatment at high temperatures; actual production and the attendant pumping problems; generator fuel type and availability; electric power requirements, design of steam injection lines; gathering lines; extent of production-injection automation; required insulation of production lines and tanks at low temperatures; and well completion methods. These are just some of the problems that need to be considered. Hence, large startup costs are always associated with steam injection methods and significant oil reserves are needed to justify the economics of such large projects.
Recently, the use of small, portable gas generators has begun in the oil and gas industry, paving the way for a new era of efficient and economical generation of flooding agents. These gas generators use rocketry engineering principles to generate flooding gases at supercritical temperatures and pressures which are injected to reenergize oil and gas fields. Such advanced recovery methods allow the oil and gas producer to recover the hydrocarbons at an accelerated rate.
2. Prior Art
As indicated, methods and apparatus are known for secondary and tertiary recovery of oil and gas from wells, and many such systems have been described in prior patented art. However, none of this prior patented art describes the process and apparatus of the present invention.
U.S. Pat. No. 4,463,803--Wytt discloses a method and apparatus for generating steam at elevated temperatures and pressures. This system utilizes a fuel, an oxidant, and water in a generator located downhole.
U.S. Pat. No. 4,475,883--Schirmer et al, discloses a bipropellant gas generating system which uses an air-fuel combustion mixture. The combustion takes place at 8% above the stoichiometric ratio (making the reaction oxygen rich), and, again, the generator is located downhole.
Martin et al, U.S. Pat. No. 4,499,946, disclose a bipropellant gas generating system capable of injecting carbon dioxide, nitrogen, and steam at elevated temperatures and pressures. The hot combustion gases are passed sequentially and selectively, and optionally through portable modular units selectively detachable, connectable to the reactor, and to each other. Such units may include a heat exchanger type of boiler to generate steam for downhole injection and/or production of power, a scrubber for removal of any particulate matter should the fuel create such; a catalytic gas purifier for removal of any corrosive material, e.g., hydrogen sulfide, sulfur, sulfur oxides, and nitrogen oxides, etc., should the fuel create such; a gas cooler; a gas drier; and a carbon dioxide absorber. This system makes no provision for the cooling of the injection well walls.
PCT application WO82/01214 in the name of Foster-Miller Associates, Inc., discloses a bipropellant gas generating system disposed downhole and relies on the combustion of an oxidant and a fuel. The gases are injected into the well formation via a converging-diverging nozzle.
A bipropellant gas generating system in which water is injected through slotted inlets along the combustion chamber wall to provide an unstable boundary layer and stripping of the water from the wall for efficient steam generation is disclosed in U.S. Pat. No. 4,385,661--Fox. Pressure responsive doors are provided at the steam outlet of the combustor assembly. The outlet doors and fluid flow functions may be controlled by a diagnostic/control module. The module is positioned in the water flow channel to maintain a relatively constant, controlled temperature.